Pandemic H1N1 Influenza A Viruses Are Resistant to the Antiviral Activities of Innate Immune Proteins of the Collectin and Pentraxin Superfamilies

Abstract

Acquired immune responses elicited to recent strains of seasonal H1N1 influenza viruses provide limited protection against emerging A(H1N1) pandemic viruses. Accordingly, pre-existing or rapidly induced innate immune defenses are of critical importance in limiting early infection. Respiratory secretions contain proteins of the innate immune system, including members of the collectin and pentraxin superfamilies. These mediate potent antiviral activity and act as an initial barrier to influenza infection. In this study, we have examined the sensitivity of H1N1 viruses, including pandemic virus strains, for their sensitivity to collectins (surfactant protein [SP]-D and mannose-binding lectin [MBL]) and to the pentraxin PTX3. Human SP-D and MBL inhibited virus-induced hemagglutinating activity, blocked the enzymatic activity of the viral neuraminidase, and neutralized the ability of H1N1 viruses to infect human respiratory epithelial cells in a manner that correlated with the degree of glycosylation in the globular head of the hemagglutinin. Recent seasonal H1N1 viruses expressed three to four N-glycosylation sequons on the head of hemagglutinin and were very sensitive to inhibition by SP-D or MBL, whereas A(H1N1) pandemic viruses expressed a single N-glycosylation sequon and were resistant to either collectin. Of interest, both seasonal and pandemic H1N1 viruses were resistant to PTX3. Thus, unlike recent seasonal H1N1 strains of influenza virus, A(H1N1) pandemic viruses are resistant to the antiviral activities of innate immune proteins of the collectin superfamily.

Addition of Glycosylation to Influenza A Virus Hemagglutinin Modulates Antibody-Mediated Recognition of H1N1 2009 Pandemic Viruses

“…RT-PCR was preformed using MyTaq One-Step RT-PCR kit (Bioline) with H1 HAI-and N1 NAI-specific primers as previously described (31). PCR products were purified and sequenced on an ABI3500XL Genetic Analyzer (Applied Biosystems), and sequences were assembled and analyzed using the Lasergene Seqman package (DNAStar7).…”

Protein glycosylation in infectious disease pathobiology and treatment

“…In a mouse model of infection, studies showed that as glycosylation was increased, disease was attenuated in part due to improved recognition and clearance by lung surfactant associated protein-D (SP-D) [52], illustrating that the addition of carbohydrate can have both positive and detrimental effects to the virus. The more recent swine 2009 H1N1 is predicted to have fewer sites for glycosylation than contemporary H1N1 strains and has been shown experimentally to have a single sequon for N-linked glycosylation on the globular head compared to seasonal H1N1 which carry 3-4 sequons [53]. Interestingly, that same study suggested that the loss of N-glycosylation led to resistance of SP-D and mannose binding lectin (MBL) activity.…”

A Single Amino Acid Substitution in the Hemagglutinin of H3N2 Subtype Influenza A Viruses Is Associated with Resistance to the Long Pentraxin PTX3 and Enhanced Virulence in Mice

“…SP-D, a major constituent of human airway fluids (45,61), is a potent inhibitor of highly glycosylated seasonal IAV; however, pandemic viruses are poorly glycosylated and, therefore, are largely resistant to this lectin (27,45,62). PTX3 acts as a SIAa(2,3)-rich "receptor decoy" that is induced following IAV infection, consistent with a role in preventing infection and limiting spread of some pandemic IAV (or avian-origin IAV) in humans.…”

“…Neutralization of virus infectivity by pentraxins was determined by fluorescent-focus reduction in monolayers of MDCK cells, as described (27). Briefly, dilutions of PTX3 or SAP, prepared in TBS containing 10 mM CaCl 2 , were incubated at 37˚C for 30 min with a standard dilution of virus and then added to MDCK cell monolayer for 1 h at 37˚C.…”